The realization of VHetNets allows the communication architecture to expand both in breadth (through extended coverage) and in-depth (through serving users at different heights), which provides the network with extra layers of connectivity, flexibility, agility, and resilience. NTNs often consist of airborne and spaceborne (satellite) communication. The deployment of standalone space-ground communication remains relatively expensive, and the path loss of satellite-to-earth links is severe. The associated space-earth inter-communication also often incurs huge delays. In contrast, the deployment of airborne stations has lower cost, reduced delay, and more favorable line-of-sight compared to TNs [1]}. The aerial layer of NTNs consists of both
HAPS and low-altitude platforms (LAPs) (e.g., unmanned air vehicles (UAVs)). Previous works in the literature study UAV-assisted wireless communication networks, where the UAV act as a flying base-station (BS) [2]}. Although such networks address some of the demands of the sixth generation of wireless networks (6G) and beyond, UAVs are energy-limited platforms and thus have short endurance. Moreover, UAVs fly in low altitudes and have a relatively small wireless footprint [1]}.
